Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual equipe visitante tem uma equipe da casa em Portland e uma data de 31 de maio?
 ###Tabelas: CREATE TABLE medal_count (medal_count_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Nation VARCHAR, Gold INT, Silver INT, Bronze INT, Total INT) CREATE TABLE intercounty_connector_bus_routes (intercounty_connector_bus_routes_id AUTO_INCREMENT PRIMARY KEY, Route VARCHAR, Terminus VARCHAR, Operated by VARCHAR, Corridors served VARCHAR, Total trips (AM/PM) VARCHAR, Operating since VARCHAR) CREATE TABLE nba_finals (nba_finals_id AUTO_INCREMENT PRIMARY KEY, Game VARCHAR, Date VARCHAR, Home team VARCHAR, Result VARCHAR, Road team VARCHAR) CREATE TABLE monthly_mobile_subscriber_additions (monthly_mobile_subscriber_additions_id AUTO_INCREMENT PRIMARY KEY, Year INT, January INT, February INT, March INT, April INT, June INT, July INT, August INT, September INT, October INT, November INT, December INT, Annual Additions(in millions) INT, Average Monthly Additions(in millions) INT) CREATE TABLE doubles:_15_9–6 (doubles:_15_9–6_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date INT, Surface VARCHAR, Partner VARCHAR, Opponents in the final VARCHAR, Score in the final VARCHAR)  
SELECT Road team FROM nba_finals WHERE Home team = portland AND Date = may 31